1. Field of the Invention
The invention relates to a process for producing a so-called "finish-effect film" having three-dimensional pores or structures that correspond to the printed area.
2. Description of the Prior Art
Finish-effect films are supporting webs, e.g., of paper, which are printed with a design, especially a wood design, and are impregnated or coated with a resin, and in which the resin is cured without pressure. These finish-effect films are then glued like wood veneers onto the surface of wood-based materials under the action of a slight pressure of ca. 5 kg/cm.sup.2. The gluing may also take place at a higher pressure by means of a resin or additional film, which serves as an adhesive and is situated on the reverse side of the finish-effect film.
In finish-effect films with a wood design, for example, it was customary until now to impress the pores by means of an embossing calender into the resin which is in a state such that it is no longer or practically non-flowable. The disadvantage of this process lies in the need to exert a mechanical stress on the web and especially in the fact that the surface structure and and the printed area do not generally coincide since, for economic reasons, it is not possible to hold the appropriate calender roll in readiness for each printed area or to carry out the calendering so as to correspond with the printing. It is an additional disadvantage that a special operating step is required for the calendering.
In recent times, various attempts have been made to produce structured films that do not have these disadvantages.
Accordingly, a process is already known from German Pat. No. 1,942,780, in which the paper is provided with a polymerization inhibitor for the coating resin at those sites at which it is to exhibit pores. This can take place by means of a printing procedure.
On subjecting the polymerization resin to curing conditions, the curing of the resin is prevented or retarded at these sites so that the unhardened polymerization resin which is still liquid can flow away either laterally or into the background to create a deficiency of cured resin on the surface at those sites where the inhibitor was present to thereby form an artificial pore.
If a polymerization inhibitor is applied by a special printing procedure at those sites of a wood design which are to have pores, pores are obtained which correspond in position with the printed area.
A disadvantage of this process, inter alia, resides in that it is restricted to using polyester resin which must be cured on the paper web by polymerization with monomeric organic compounds, such as, for example, styrene. Some of these monomers are volatile under curing conditions and special precautions must be taken because of the flammability of these volatile components. Also, such monomers are physiologically harmful.
In addition, the process is cumbersome and difficult to carry out in practice, as is evident from a description in the journal "Japan Plastics Industrial Annual," 1975, Page 64. There is a further description of the process in the published Japanese patent application No. 28 262/74. It is particularly disadvantageous in that, that products obtained by using paper according to this process are not resistant to splitting or delamination so that the surface can easily be separated from the substrate by appropriate mechanical stresses.
A chemical embossing process is known from German Auslegeschrift No. 1,277,721, in which a foam inhibitor or retarder is printed according to a design into a foamable plastic layer so that surface regions of different thickness result.
Another process for producing synthetic resin imitation wood grained surfaces is described in U.S. Pat. No. 3,811,915. According to this process, the paper web is initially provided with a coating, which is allowed to dry whereupon it is printed with a printing ink, which causes the pore formation and which contains 0.1 to 3% by weight of a liquid silicone. The supporting web is then coated with a conventional resin coating. In this process, use is made of the effect that the silicone containing printing ink leads to wetting obstructions for the final coating, so that there is a deficiency of resin at those sites in the surface at which the silicon containing dye is present and a pore structure is produced by physical means.
It is a particular disadvantage of this process that the supporting web which is printed with a printing ink containing silicone, must be coated with resin within at most 20 hours since the effect is no longer observed after this time.